Exposure method and apparatus having a decreased light intensity distribution

ABSTRACT

A method and apparatus for transferring a fine pattern ( 12 ) on a mask ( 11 ) onto a substrate ( 17 ) by a projection exposure apparatus including an illumination optical system ( 1 - 10 ) for irradiating an illuminating light on the mask ( 11 ), and a projection optical system ( 13 ) for projecting an image of the fine pattern ( 12 ) on the illuminated mask onto the substrate ( 17 ). The illuminating light is irradiated at least in the form of a pair of light beams opposedly inclined with respect to the mask through a pair of transparent windows ( 6   a,    6   b ) of a spatial filter ( 6 ) whereby either one of the ±first-order diffracted beams and the 0-order diffracted beam produced from the fine pattern ( 12 ) of the mask ( 11 ) illuminated by each light beam are respectively passed apart by the equal distance from the optical axis of the projection optical system at or near to the Fourier transform plane within the projection optical system with respect to the fine pattern ( 12 ) of the mask ( 11 ), thereby forming on the substrate ( 17 ) a high-resolution projected image of a strong light-and-dark contrast with a high degree of focus depth.

This is a Continuation of application Ser. No. 08/485,791 filed Jun. 7,1995, now abandoned which in turn is a Continuation of application Ser.No. 08/257,956, filed Jun. 10, 1994 now U.S. Pat. No. 9,658,211, whichis in turn a Continuation of application Ser. No. 08/101,674, nowabandoned filed Aug. 4, 1993, which in turn is a Continuation ofapplication Ser. No. 07/847,030, filed Apr. 15, 1992 now abandoned.

TECHNICAL FIELD

The present invention relates to an exposure method and apparatus andmore particularly to a projection exposure method and apparatus used inthe lithographic operation for semiconductor memory devices and liquidcrystal devices having regular fine patterns.

BACKGROUND ART

In the manufacture of semiconductor memory devices and liquid crystaldevices by photolithographic techniques, the method of transferring amask pattern onto a substrate has been generally used. In this case, theilluminating light for exposure purposes, e.g., ultraviolet light isirradiated on the substrate having a photosensitive resist layer formedon its surface through a mask formed with a mask pattern and thus themask pattern is photographically transferred onto the substrate.

The common type of the fine mask patterns for semiconductor memorydevices, liquid crystal devices, etc., can be considered as regulargrating patterns which are vertically or laterally arranged at equalintervals. In other words, in the mask pattern of this type the mostdense pattern area is formed with a grating pattern composed ofequally-spaced transparent and opaque lines which are alternatelyarranged in the X-direction and/or the Y-direction to realize theminimum possible line width which can be formed on the substrate and theother area is formed with a pattern of a comparatively low degree offineness. Also, in any case any oblique pattern is exceptional.

Further, the ordinary photosensitive resist material has a non-linearlight response characteristic so that the application of a lightquantity greater than a certain level causes chemical changes to proceedrapidly, whereas practically the chemical changes do not progress whenthe quantity of light received is less than this level. As a result,there is a background that with the projected image of the mask patternon the substrate, if the difference in light quantity between the lightand dark portions is ensured satisfactorily, even if the contrast of theboundary between the light and dark portions is low more or less, thedesired resist image as the mask pattern can be obtained.

With the recent tendency toward finer pattern structures forsemiconductor memories and liquid crystal devices, projection exposureapparatus such as a stepper for transferring a mask pattern onto asubstrate by reduction projection have been used frequently and aspecial ultraviolet light which is shorter in wavelength and narrow inwavelengh distribution range has also come into use as an exposureilluminating light. In this case, the reason for reducing the wavelengthdistribution range resides in eliminating any deterioration in the imagequality of a projected image due to the chromatic aberrations of theprojection optical system in the exposure apparatus and the reason forselecting the shorter wavelength is to enhance the contrast of theprojected image. However, the actual situation is such that this attemptof reducing the wavelength of an illuminating light has reached thelimit with respect to the requirements for finer mask patterns, e.g.,the projection exposure of line width of the sub-micron order due to thenon-existence of any suitable light source, the restrictions to lensmaterials and resist materials, etc.

In the case of such a finer mask pattern, the required value for theresolution (line width) of the pattern approaches the wavelength of theilluminating light so that the effect of the diffracted light producedby the transmission of the illuminating light through the mask patterncannot be ignored and it is difficult to ensure a satisfactorylight-and-dark contrast of the projected mask pattern image on thesubstrate, thereby particularly deteriorating the light-and-darkcontrast of the line edges of the pattern.

In other words, while the diffracted beams of the 0-order,±first-orders, ±second-orders and higher-orders produced at variouspoints on the mask pattern by the illuminating light incident on themask from above are respectively reconverged at the correspondingconjugate points on the substrate for imaging through the projectionoptical system, the diffracted beams of the ±first-orders,±second-orders and higher-orders are further increased in diffractionangle as compared with the diffracted beam of the 0-order and areincident on the substrate at smaller angles for the finer mask pattern.This gives rise to a problem that the focus depth of the projected imageis decreased greatly and a sufficient exposure energy is supplied onlyto a portion of the thickness of the resist layer.

As a measure for coping with such decrease in the focus depth, JapaneseLaid-Open Patent Application No. 2-50417 (laid open on Feb. 20, 1990)discloses the method of arranging an aperture stop concentrically withthe optical axis of each of an illumination optical system and aprojection optical system to restrict the angles of incidence of anilluminating light on a mask and adjusting the opening diameters of theaperture stops in accordance with a mask pattern. This ensures the focusdepth while maintaining the light-and-dark contrast of a projected imageon a sample substrate. Even in the case of this known method, however,the diffraction angles of diffracted beams of the ±first-orders andhigher-orders are still large as compared with a 0-order diffracted beamreaching substantially vertically to the surface of a substrate andpractically all of them come out of the field of view of a projectionlens, thereby producing on the substrate only a projected mask patternimage composed by substantially only the 0-order beam component andhaving a weak contrast.

Also, while, in this case, there is the possibility of a part of the±first-order diffracted beams coming within the field of view of theprojection lens and reaching the substrate, in contrast to the 0-orderdiffracted beam incident substantially vertically on the substrate, thepart of the ±first-order diffracted beams is incident on the substrateat a smaller angle and therefore it is pointed out that a satisfactoryfocus depth is still not obtainable.

On the other hand, U.S. Pat. No. 4,947,413 granted to T. E. Jewell etall discloses a lithography system in which an off-axis illuminationlight source is used and an interference of the 0-order diffracted beamand only one of the ±first-order beams from a mask pattern is madepossible by use of a spatial filter processing in the Fourier transformplane within a projection optical system, thereby forming ahigh-contrast projected pattern image on the substrate with a highdegree of resolution. With this system, however, the illumination lightsource must be arranged in an off-axis position in which it is obliquelydirected to the mask, and also due to the fact that the 0-orderdiffracted beam and only one of the ±first-order diffracted beams aresimply caused to interfere with each other, the dark-and-light contrastof the edges in the pattern image resulting from the interference isstill unsatisfactory due to the unbalanced light quantity differencebetween the 0-order diffracted beam and the first-order diffracted beam.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a projectionexposure method and apparatus so designed that a projected image havinga sufficient light-and-dark contrast is produced with a large focusdepth on a substrate from the fine mask pattern of the ordinary maskhaving no phase shifting means, and more particularly it is an object ofthe invention to positively utilize the fact that the illuminating lighthas a narrow wavelength distribution, that the mask pattern can besubstantially considered to be a diffraction grating, that the resistmaterial has a non-linear light responsive characteristic for the amountof light received and so on as mentioned previously so as to form aresist image of a finer mask pattern for the same wavelength of theilluminating light.

In accordance with a basic idea of the present invention, when using anexposure apparatus including an illumination optical system forilluminating a mask formed at least partially with a fine pattern withan illuminating light and a projection optical system for projecting animage of the illuminated fine pattern on a substrate so as to transferthe fine pattern of the mask on the substrate, the illuminating light isdirected from at least two locations to fall on the mask with givenangles of incidence in an obliquely opposing manner so that the 0-orderdiffracted beam and either one of ±first-order diffracted beams producedfrom the fine pattern by each of the obliquely illuminating beams arerespectively passed through optical paths which are substantiallyequidistant from the optical axis of the projection optical system at orin the vicinity of the Fourier transform plane within the projectionoptical system with respect to the fine pattern on the mask, therebyforming on the substrate a projected image of the fine patternprincipally by either of the ±first-order diffracted beams and the0-order diffracted beam. In this case, the other undesired beamsexcluding either of the ±first-order diffracted beams and the 0-orderdiffracted beam do not substantially reach the substrate. As opticalmeans for this purpose, principally spatial filter means is arranged inthe illumination optical system and/or the projection optical system.Also, the illumination optical system can be constructed so as to directthe illuminating light along its optical axis and the illuminationoptical system includes an optical element, e.g., condenser lens meansarranged on this side of the mask such that the illuminating light fallsat the given angles of incidence on the mask.

An exposure apparatus according to a preferred aspect of the presentinvention includes an illumination optical system for irradiating anilluminating light on a mask, a projection optical system for projectingan image of the fine pattern on the illuminated mask onto a substrateand spatial filter means arranged at or in the vicinity of the Fouriertransform plane within the illumination optical system and/or theprojection optical system with respect to the fine pattern on the mask,and the spatial filter means includes at least two window means whichare each defined by an independent limited area having a comparativelyhigher light transmittance than the surrounding at a position apart fromthe optical axis of the illumination optical system and/or theprojection optical system in which it is arranged. The Fourier transformplane at which the spatial filter means is arranged is placed forexample in a position that is practically in the pupil plane of theillumination optical system, the conjugate plane to the aforesaid pupilplane or the pupil plane of the projection optical system, and thespatial filter means can be arranged at least in one of these positions.

In accordance with another preferred aspect of the present invention,the spatial filter means includes the two window means at substantiallythe symmetric positions with the optical axis of the illuminationoptical system and/or the projection optical system in which it isarranged.

In accordance with another preferred aspect of the present invention,the number of the window means in the spatial filter means is 2n (n is anatural number). Also, the window means is preferably arranged at eachof a plurality of positions determined in accordance with the Fouriertransform pattern of the fine pattern.

In accordance with another aspect of the present invention, theillumination optical system includes an optical integrator, e.g.,fly-eye lenses and in this case the spatial filter means is arranged ina position near to the exit end of the optical integrator.

In accordance with the present invention, the portion of the spatialfilter means excluding the window means is generally formed as a darkportion or a light shielding portion whose light transmittance issubstantially 0% or so or alternatively it is formed as a lightattenuating portion having a predetermined light transmittance which islower than that of the window means.

In accordance with another aspect of the present invention, the spatialfilter means is arranged within the illumination optical system and thepositions of its window means are selected such that either one of the±first-order diffracted beams and the 0-order diffracted beam due toeach window means are respectively passed through positions which arepractically apart by the equal distance from the optical axis of theprojection optical system at or in the vicinity of the Fourier transformplane within the projection optical system with respect to the finepattern on the mask.

In accordance with another preferred aspect of the present invention,the spatial filter means is arranged within the illumination opticalsystem and the spatial filter means includes first and second windowmeans forming a symmetrical pair with respect to the optical axis of theillumination optical system, with the positions of the first and secondwindow means being so determined that the two diffracted beams, i.e.,either one of the ±first-order diffracted beams and the 0-orderdiffracted beam produced from the fine pattern by the irradiation of theilluminating light beam reaching the mask through the first window meansand another two diffracted beams, i.e., either one of the ±first-orderdiffracted beams and the 0-order diffracted beam produced from the finepattern by the irradiation of the illuminating light beam reaching themask through the second window means are alternatively passed throughseparate first and second optical paths which are apart by practicallythe equal distance from the optical axis of the projection opticalsystem at or positions near to the Fourier transform plane within theprojection optical system, that is, the two diffracted beams, i.e.,either one of the ±first-order diffracted beams due to the illuminatinglight from the first window means and the 0-order diffracted beam due tothe illuminating light through the second window means are for examplepassed through the first optical path and either one of the ±first-orderdiffracted beams due to the illuminating light through the second windowmeans and the 0-order diffracted beam due to the illuminating lightthrough the first window means are for example passed through the secondoptical path.

In accordance with another preferred aspect of the present invention,the exposure apparatus includes drive means for varying at least one ofthe angular positions of the window means about the optical axis andtheir distance apart from the optical axis in accordance with the finepattern on the mask for adjusting or switching purposes. Where thespatial filter means comprises a light shielding plate or lightattenuating plate including a plurality of window means, the drive meanscomprises a mechanism for replacing the light shielding plate or thelight attenuating plate with one having window means at differentpositions, whereas if the spatial filter means comprises an electroopticelement which is capable of making transparent or opaque the limitedareas at arbitrary positions, such as, a liquid crystal device or anelectro chromic device, the drive means comprises electric circuit meansfor driving the electrooptic element for the purpose of making thelimited areas transparent or opaque.

The conventional projection exposure apparatus uses indiscriminately anilluminating light which falls at various angles of incidence on a maskfrom above so that the respective diffracted beams of the 0-order,±first-orders, ±second-orders, and higher-orders produced from the maskpattern are directed in practically disordered directions and thepositions at which these diffracted beams are imaged through theprojection optical system on a substrate are different from one another.On the other hand, the projection exposure apparatus of the presentinvention selectively uses the illuminating light which is incident on amask pattern with specified directions and angles from the givenpositions within a plane intersecting the optical axis at right anglesso that either one of the ±first-order diffracted beams and the 0-orderdiffracted beam produced from the mask pattern by each illuminating beamare mainly directed onto the substrate and chiefly participate in theformation of a projected image of the fine pattern on the substrate. Inother words, in accordance with the present invention the spatial filtermeans corresponding to the mask pattern is used for this purpose so thatonly optimum one of the ±first-order diffracted beams and the 0-orderdiffracted beam by each illuminating beam are mainly selected from theilluminating light by the spatial filter means and are directed onto thesubstrate, thereby forming on the substrate a projected pattern imagewhich is higher in the light-and-dark contrast of the edges of the finepattern than previously and which is large in focus depth.

In this connection, there are the following two methods for theapplication of the spatial filter means according to the presentinvention. More specifically, the first method is such that theilluminating light is intercepted or attenuated at a portion of its beamcross-section on this side of the mask so as to select, as the principalilluminating light, the illuminating light obliquely incident with thespecified direction and angle from each of the given positions withinthe plane intersecting the optical axis at right angles, and for thispurpose the spatial filter means is arranged at the Fourier transformplane within the illumination optical system or a position near thereto.The second method is such that of the various diffracted beam componentsproduced from the mask pattern illuminated by the illuminating light ofvarious angles of incidence, the two component beams or either one ofthe ±first-order diffracted beams and the 0-order diffracted beamproduced from the mask pattern by each of the illuminating beamsincident obliquely with the given directions and angles from the givenpositions within the plane intersecting the optical axis at right anglesare selected within the projection optical system, and for this purposethe spatial filter means is arranged at the Fourier transform planewithin the projection optical system or a position near thereto. Thesefirst and second methods may be used in combination and in any way thespatial filter means serves the role of limiting the light beamsparticipating in the formation of a projected pattern image on thesubstrate to either one of the ±first-order diffracted beams and the0-order diffracted beam produced from the mask pattern by each of theilluminating beams which are incident obliquely with the specifiedinclination angles and preventing the other undesired beams fromreaching the substrate.

Where the spatial filter means is arranged at the Fourier transformplane within the illumination optical system or a position near thereto,the illuminating light having a given wavelength is projected onto themask pattern in the form of a diffraction grating with the given anglesof incidence from the given eccentric positions in the given angulardirections about the optical axis so that theoretically a series ofspots due to the Fourier expanded 0-order, first-orders, second-ordersand higher-orders diffracted beams are formed at the Fourier transformplane of the projection optical system or positions near thereto. In theconventional projection exposure apparatus, however, the second-ordersand higher-orders diffracted beams are eclipsed by the lens tube of theprojection optical system.

The spatial filter means arranged at the Fourier transform plane withinthe illumination optical system or a position near thereto is alsodesigned so that the illuminating light falling substantially verticallyon the mask is intercepted or attenuated and that the illuminating lightto be incident on the mask at the given angles of inclination from thegiven eccentric positions in the given angular directions about theoptical axis is selectively passed with a high light transmittance. Inthis case, if the diffracted beams of the second-orders andhigher-orders are not desired, another spatial filter means is furtherprovided at the Fourier transform plane within the projection opticalsystem or in the vicinity thereof to block or attenuate these beams. Asa result, a high-contrast projected pattern image is formed on thesubstrate by the 0-order diffracted beam and the first-order diffractedbeams produced from the mask pattern by the illuminating light at thepreferred angles of incidence.

Then, with the mask patterns for semiconductor memory devices and liquidcrystal devices, there are many cases where the portion of the maskpattern requiring a high-resolution transfer has a pattern composed of agrating pattern in which basically equispaced transparent and opaquelines are regularly arranged alternately and this can be generallyconsidered to be a repetition pattern of rectangular waveforms at theduty ratio of 0.5. Where the spatial filter means is arranged at theFourier transform plane within the illumination optical system or aposition near thereto, due to the diffracted beams produced from thegrating pattern, a series of spots of the diffracted beams of the0-order, ±first-orders, ±second-orders and higher-orders are formed atthe Fourier transform plane of the projection optical system so as to bedistributed in the direction of traversing the lines of the grating (thedirection in which the lines are arranged). At this time, in the likemanner known as the ordinary Fourier expansion of a rectangular wave,the 0-order diffracted beam provides a reference level for the lightquantity in the projected image on the substrate and the ±first-orderdiffracted beams are the light quantity variation components of thesinusoidal waveform having the same period as the grating, so that whenthese diffracted beam components are condensed on the substrate, theinterference of these diffracted beams produces on the substrate animaged pattern having a sufficient light quantity for the sensitizationof the resist layer and a high light-and-dark contrast.

Also, in this case the ordinary mask pattern for semiconductor memorydevices and liquid crystal devices can be considered to be a combinationof a plurality of gratings which are respectively arranged vertically ortransversely on the mask so that if spatial filter means is prepared soas to ensure illuminating light beams having the optimum eccentricpositions in the angular directions about the optical axis and theoptimum angles of incidence for each grating, the resulting Fourierpattern formed at the Fourier transform plane of the projection opticalsystem forms a spot group arranged in the angular directionscorresponding to the line arranging directions of the gratings andhaving the spacings corresponding to the wavelength of the illuminatinglight and the line pitches of the gratings. The light intensity of eachspot is dependent on the number of pitches of the gratings and theorders of the diffracted beams.

As will be seen from this fact, the same effect can be obtained byarranging within the projection optical system spatial filter meansformed with window means only at the positions corresponding to therequired spot positions so as to select the diffracted beams directed tothe substrate. In this case, the spatial filter means arranged at theFourier transform plane or a position near thereto includes the windowmeans at the spot positions of the useful diffracted beams in theFourier transform plane so that the useful diffracted beams areselectively passed while blocking the undesired diffracted beams whichcause deterioration of the contrast at the substrate surface.

Thus, the number and positions of the windows in the spatial filtermeans inherently differ depending on the mask pattern so that when themask is changed, the spatial filter means is also changed in companytherewith as a matter of course and moreover it must be exactly adjustedin position relative to the mask.

Next, a description will be made of the reason why the focus depth isincreased by projecting the illuminating light beams of the given anglesof incidence onto the mask pattern from the given eccentric positions inthe given angular directions about the optical axis and forming animaged pattern on the substrate by means of either one of the±first-order diffracted beams and the 0-order diffracted beam producedfrom the mask pattern by each of the illuminating light beams.

Generally, where the substrate is in registration with the focalposition of the projection optical system, the diffracted beams of therespective orders which emerge from one point on the mask and reach onepoint on the substrate are all equal in optical path length irrespectiveof the portions of the projection optical system through which they passso that even in cases where the 0-order diffracted beam passes throughpractically the center of the pupil plane of the projection opticalsystem, the 0-order diffracted beam and the diffracted beams of theother orders are equal in optical path length and, with the optical pathlength of the light beam passing through practically the center of theFourier transform plane being taken as a reference, the differencebetween the optical path length of the light beam passing through anyarbitrary position of the Fourier transform plane and the referenceoptical path length or the front wave aberration is zero. Where thesubstrate is in a defocus position which is not in registration with thefocal position of the projection optical system, however, the opticalpath length of the diffracted beam having any of the first and higherorders and passing any closer-to-outer-periphery portion of the Fouriertransform plane within the projection optical system to fall obliquelyon the substrate is decreased as compared with the 0-order diffractedbeam passing through or near the center of the Fourier transform planewhen the substrate is positioned before the focal point and the amountof defocus is negative, whereas it is increased when the substrate ispositioned in the rear of the focal point and the amount of defocus ispositive; this difference in optical path length has a valuecorresponding to the difference in angle of incidence on the substratebetween the diffracted beams of the respective orders and this isreferred to as the front wave aberration due to the defocus. In otherwords, due to the presence of such defocus, each of the diffracted beamsof the first and higher orders causes a front wave aberration withrespect to the 0-order diffracted beam and the imaged pattern in eitherthe front or the rear of the focal point is blurred. This front waveaberration ΔW is given by the following equation

ΔW=1/2 ×(NA)² ·Δf

where

Δf=the amount of defocus

NA=the value of the distance from the center in the Fourier transformplane given in terms of the numerical aperture.

As a result, in relation to the 0-order diffracted beam (ΔW=0) passingthrough practically the center of the Fourier transform plane, thefirst-order diffracted beam passing through the position of a radius r₁near the outer periphery of the Fourier transform plane has thefollowing front wave aberration

ΔW=1/2×r ₁ ^(2×Δ) f

and the presence of this front wave aberration is the cause ofdeterioration of the resolution before and behind the focal position andreduction in the focus depth in the conventional techniques.

On the other hand, in the exposure apparatus of the present inventionthe spatial filter means is arranged such that either one of the±first-order diffracted beams and the 0-order diffracted beam producedfrom the mask pattern by each of the illuminating light beams of thegiven angles of incidence are respectively passed through the eccentricpositions (having the same eccentric radius r₂) of substantially thecentral symmetry in the Fourier transform plane within the projectionoptical system. As a result, in the case of the exposure apparatus ofthe present invention the front wave aberrations caused by the 0-orderdiffracted beam and the first-order diffracted beams before and behindthe focal point of the projection optical system are both given asfollows

ΔW=1/2×r ₂ ² Δf

and they are equal to each other. Thus, there is no deterioration (blur)of the image quality caused by the front wave aberrations due to thedefocus, that is, the correspondingly increased focus depth is obtained.

On the other hand, where the spatial filter means is arranged within theillumination optical system, a pair of the illuminating light beamspassed through the pair of the window means symmetric with the opticalaxis take the form of light beams which are incident on the mask surfaceobliquely and symmetrically on both sides of the normal so that each oneof the ±first-order diffracted beams produced from the grating patternon the mask by these light beams passes a position which is symmetricwith the 0-order diffracted beam with respect to the optical axis of theprojection optical system and falls on the substrate at an angle ofincidence as large as that of the 0-order diffracted beam. As a result,the substantial numerical aperture of the projection optical systemparticipating in the imaging is reduced thereby ensuring a greater focusdepth.

Thus, in accordance with the present invention, by virtue of the factthat the spatial filter means having the windows of the paired structureon both sides of the optical axis is used such that, of the diffractedbeams produced from the fine pattern on the mask by the illuminatinglight beams of the preferred angles of incidence, the diffracted beamsof the preferred orders, i.e., the 0-order diffracted beam and thefirst-order diffracted beams are selectively condensed at the sameposition on the substrate so that even in the case of such fine patternwhich has never been resolved in the past, it is now possible to ensurea satisfactory light-and-dark contrast and a satisfactorily large focusdepth for sensitizing the resist layer in the imaged pattern on thesubstrate without any change of the illuminating light and theprojection optical system.

Where the spatial filter means is arranged within the illuminationoptical system, the spacing between the pair of windows in the spatialfilter means is such that either one of the ±first-order diffractedbeams produced from the fine grating pattern of the mask by theilluminating light passing through one of the windows and the 0-orderdiffracted beam produced by the illuminating light passing through theother window are passed through substantially the same eccentricposition in the Fourier transform plane of the projection opticalsystem.

Where the spatial filter means is arranged within the projection opticalsystem, the spacing between the pair of windows in the spatial filtermeans is determined in such a manner that either one of the ±first-orderdiffracted beams and the 0-order diffracted beam produced from the finegrating pattern of the mask by each of the illuminating beams of thepreferred angles of incidence are respectively passed through separateeccentric positions.

In accordance with the exposure apparatus of the present invention, asuitable adjusting mechanism is used so that the spatial filter means isrotated through a certain angle or parallelly moved within the plane ofits arrangement so as to compensate for the shifts in the positions ofthe windows of the spatial filter means relative to the mask pattern.Also, the spacing between the pair of windows may be constructed so asto be adjustable to conform more satisfactorily with the Fourier patternof the mask pattern. In this case, by constructing so that the positionsof the windows in the spatial filter or the spacing between the windowscan be varied by the adjusting mechanism, it is possible to obtain theoptimal positional relation between the mask and the windows of thespatial filter and also it is possible to use the same spatial filter incommon with other masks containing different patterns.

In accordance with another aspect of the present invention, a spatialfilter incorporating an electrooptical element such as a liquid crystaldevice or an electro chromic device is employed so that the adjustmentof the positions and size of its windows can be effected by means ofelectric signals. In this case, due to the fact that the limited areasat the arbitrary positions of the spatial filter composed of theelectrooptical element can be freely adjusted to become transparent oropaque, it is possible to obtain the optical positional relation betweenthe mask pattern and the windows of the spatial filter and in this caseit is of course possible to use the same spatial filter in common withother masks containing different patterns.

In order to facilitate the understanding of the above and other featuresand advantages of the present invention, some preferred embodiments ofthe invention will be described hereunder with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing the construction of an exposureapparatus according to an embodiment of the present invention,

FIG. 2 is a schematic diagram showing an optical path construction forexplaining the principle of the embodiment of FIG. 1,

FIG. 3 is a plan view showing an example of the spatial filter arrangedwithin the illumination optical system of the exposure apparatusaccording to the embodiment of FIG. 1,

FIG. 4 is a schematic plan view showing an example of the mask pattern,

FIGS. 5a and 5 b are schematic plan views showing respectively otherexamples of the spatial filter,

FIGS. 6a and 6 b are diagrams showing schematically the light intensitydistributions of the diffracted beams at the Fourier transform plane ofthe projection optical system in correspondence to FIGS. 5a and 5 b,respectively,

FIG. 7 is a schematic diagram showing the optical path construction of aprojection exposure apparatus according to a reference example,

FIG. 8 is a diagram showing schematically the intensity distribution ofthe diffracted beams at the Fourier transform plane of the projectionoptical system in FIG. 7,

FIG. 9 is a schematic diagram showing the optical path construction of aprojection exposure apparatus according to another reference example,

FIG. 10 is a diagram showing in a schematic diversified form theintensity distribution of the diffracted beams at the Fourier transformplane of the projection optical system in the reference example of FIG.9,

FIG. 11 is a graph showing the light quantity distribution of theprojected image in the embodiment of the present invention,

FIG. 12 is a graph showing the light quantity distribution of theprojected image in the reference example of FIG. 7 (where σ=0.5),

FIG. 13 is a graph showing the light quantity distribution of theprojected image in the reference example of FIG. 7 (where σ=0.9), and

FIG. 14 is a graph showing the light quantity distribution of theprojected image in the reference example of FIG. 9.

BEST MODE FOR CARRYING OUT THE INVENTION

In the Embodiment shown in FIG. 1, a mask 11 is formed with aone-dimensional grating pattern 12 having a duty ratio of 0.5 as atypical exemplary fine pattern. An illumination optical system forilluminating the mask 11 includes a mercury vapor lamp 1, an ellipsoidalmirror 2, a cold mirror 3, a condensing optical element 4, an opticalintegrator element 5, a relay lens 8 (a pupil relay system), a mirror 9.A and a condenser lens 10, and a spatial filter 6 is arranged at theFourier transform plane of the illumination optical system or in thevicinity of the exit end of the integrator element 5 where the secondarylight source image of the mercury vapor lamp 1 is formed (in otherwords, the pupil plane of the illumination optical system or itsconjugate plane or any position near thereto). The spatial filter 6 isformed with a pair of transparent windows 6 a and 6 b whose positionsand size are determined in accordance with the two-dimensional Fouriertransform of the mask pattern 12.

Also, a spatial filter 15 having similarly a pair of transparent windows15 a and 15 b is arranged at the Fourier transform plane 14 of aprojection optical system 13 for projecting an image of the pattern 12onto a wafer 17. Since a one-dimensional diffraction grating pattern isused as the pattern 12 in the present embodiment, the spatial filters 6and 15 are each formed with the pair of transparent windows 6 a and 6 bor 15 a and 15 b respectively so that each pair of transparent windowsare placed in practically symmetrical positions on both sides of theoptical axis of the optical system and their direction of arrangementcoincides optically with the line pitch direction of the grating pattern12 within the plane of arrangement thereof. Also, the spatial filters 6and 15 are respectively provided with driving mechanisms 7 and 16 eachcomposed of a motor, a cam, etc., so that the spatial filters 6 and 15are replaceable with different ones depending on the mask pattern andthe positions of the transparent windows 6 a and 6 b or 15 a and 15 bcan undergo fine adjustment within the plane of arrangement of eachspatial filter. It is to be noted that the opening shape of thetransparent windows 6 a, 6 b and 15 a, 15 b of the spatial filters 6 and15 can be determined arbitrarily and in FIG. 1 they are shown as havingcircular openings by way of example without any intention of limitingthereof. Further, while the spatial filters 6 and 15 are each composedof a light shielding plate 6 c formed with a pair of openings astransparent windows, the spatial filters 6 and 15 may each be composedof an electrooptic element such as a liquid crystal device or electrochromic device and in this case each of the illustrated drivingmechanisms 7 and 16 is composed of electric circuitry 34 for causing atransparent portion of a suitable size and shape at each of arbitrarylimited areas 32 a and 32 b of the electrooptical element 32.

With the exposure apparatus constructed as described above, theilluminating light produced from the mercury vapor lamp 1 arranged atthe first focal point of the ellipsoidal mirror 2 is reflected by theellipsoidal mirror 2 and the cold mirror 3 so that after theilluminating light has been condensed at the second focal point of theellipsoidal mirror 2, it is passed through the condensing opticalelement 4 composed for example of a collimator lens or light beamdistribution compensating cone prism and through the integrator element5 comprising a group of fly-eye lenses thereby forming a substantialplane source of light in the plane of arrangement of the spatial filter6. It is to be noted that in the present embodiment the so-calledKöhler's illumination is used in which the secondary light source imageof the integrator element 5 is formed at the Fourier transform plane 14of the projection optical system 13. While this plane light sourceitself should project the illuminating light at various angles ofincidence onto the mask from above as in the past, since the spatialfilter 6 is arranged on this side of the condenser lens 10 in this case,only the collimated light beams passing through the transparent windows6 a and 6 b of the spatial filter 6 fall on the mask 11 at given obliqueangles of incidence and symmetrically with the optical axis within theplane crossing the lines of the grating pattern 12 through the relaylens 8, the mirror 9 and the condenser lens 10.

When the collimated beams are projected onto the pattern 12 of the mask11, diffracted beams of the 0-order, ±first-orders, ±second-orders andhigher-orders are produced from the pattern 12. Here, since thetransparent windows 6 a and 6 b of the spatial filter 6 arranged at theFourier transform plane 14 of the illuminating optical system determinethe distances of the collimated light beams from the optical axis aswell as their positions about the optical axis and the condenser lens 10determines the angles of incidence of the collimated light beams ontothe pattern 12 of the mask 11, of the diffracted beams of the variousorders those directed to the projection optical system 13 from eachwindow are practically only either one of the ±first-order diffractedbeams and the 0-order diffracted beam and the other diffracted beams arevery small in quantity. As a result, principal diffracted beam spots dueto either of the ±first-order diffracted beams and the 0-orderdiffracted beam and diffracted beam spots of the other undesired ordersare formed at the Fourier transform plane of the projection opticalsystem 13 in accordance with the Fourier expanded pattern. The otherspatial filter 15 arranged at the Fourier transform plane 14 of theprojection optical system 13 selectively passes only the principaldiffracted beams toward the wafer 17 and intercepts the diffracted beamsof the other undesired orders. In this case, the positions of thespatial filters 6 and 15 are adjusted relative to the pattern 12 of themask 11 by the driving mechanisms 7 and 16, respectively, so that theprincipal diffracted beams or either of the ±first-order diffractedbeams and the 0-order diffracted beams are passed with the maximumintensity and the other undesired diffracted beams are blockedcompletely.

FIG. 2 shows schematically the basic optical path construction for theilluminating light in the exposure apparatus according to the presentembodiment. While, in the Figure, the spatial filter 6 is arranged justabove the condenser lens 10 for purposes of illustration, this positionis a conjugate plane to the spatial filter 6 of FIG. 1 with respect tothe relay lens 8 and this construction is substantially the same infunction and effect with the case of FIG. 1.

In FIG. 2, if NA represents the numerical aperture of the projectionoptical system and λ the wavelength of the illuminating light, the pitchof the pattern 12 is selected to be 0.75 times λ/NA and theline-to-space ratio of the pattern 12 is selected 1:1 (the duty ratio ofthe grating is 0.5). In this case, with the wavelength λ taken intoconsideration, the Fourier transform q(u, v) of the pattern 12 is givenas follows if the pattern 12 is represented by p(x, y)

q(u,v)=p(x,y)·exp{−2πi(ux+vy)/λ}dxdy

Also, where the pattern 12 is uniform vertically or in the y-directionand varies regularly in the x-direction as shown in FIG. 4, if thex-direction line-to-space ratio is 1:1 and the line pitch is 0.75λ/NA,the following equation holds

q(u,v)=q ₁(u)×q ₂(v)

therefore, the following hold

 q ₁(u)=1, u=0

q ₁(u)=0.637, u=±NA/0.75

q ₁(u)=−0.212, u=±3 NA/0.75 . . .

q ₁(u)=0.637/(2n−1)(−1)^((n+1)) , u=±(2n−1)·NA/0.75

q ₁(u)=0, u is other than the foregoing

and

q ₂(v)=1, v=0

q ₂(v)=0, v≠0

FIGS. 3 and 5a are respectively plan views of the spatial filter 6 forthe illumination optical system and the spatial filter 15 for theprojection optical system which are used in the present embodiment.

The spatial filters 6 and 15 are such that with the following showingthe peak values of the Fourier transform energy distribution |q(u,v)|²

(u,v)=(0, 0),(±NA/0.75, 0),(±3 NA/0.75, 0) . . .

and with the following showing 1/2 thereof

(u,v)=(0, 0),(±NA/1.5, 0), (±2 NA, 0) . . .

the positions falling within the numerical aperture of the projectionoptical system 13 or the following

(u,v)=(±NA/ 1.5, 0)

or their nearby positions are selected to be the transparent windows 6a, 6 b and 15 a, 15 b, respectively, and the positions or the followingare selected to be the light shielding portions.

(u,v)=(0, 0)

It is to be noted that the positions of the spatial filters 6 and 15 orthe following are respectively adjusted by the driving mechanisms 7 and16 of FIG. 1 so as to coincide with the optical axes of the illuminationoptical system (1 to 10) and the projection optical system 13,respectively. Each of the spatial filters 6 and 15 may for example becomposed of an opaque metal sheet which is selectively removed to formits transparent windows or a transparent holding sheet coated with athin film of metal or the like by patterning to form its transparentwindows. Also, while, in the embodiment shown in FIG. 1, theilluminating light source comprises the mercury vapor lamp 1, it may becomposed of any other light source such as a laser light source.Further, while, in this embodiment, the pattern 12 of the mask 11comprises a line-and-space pattern varying only in the x-direction at aduty ratio of 1:1, the present invention is also applicable to otherpatterns varying in a plurality of arbitrary directions regularly.

In FIG. 2, as the result of the arrangement of the illustrated spatialfilter 6 at the Fourier transform plane of the pattern 12 within theilluminating optical system for the pattern 12 having the line pitch of0.75λ/NA, the illuminating light Li for illuminating the pattern 12 islimited for example to collimated light beams Lil and Lir. When theilluminating beams Lil and Lir are projected onto the pattern 12, theirdiffracted beams are produced from the pattern 12.

Assuming that the 0-order diffracted beam and the +first-orderdiffracted beam of the illuminating beam Lil are respectivelyrepresented as Ll0 and Ll1 and the 0-order diffracted beam and the−first-order diffracted beam of the illuminating beam Lir as Lr0 andLr1, the deviation angles between the diffracted beams Ll0 and Ll1 andbetween diffracted beams Lr0 and Lr1 are both given by the following$\begin{matrix}{{\sin \quad \theta} = {\lambda/\left( {{line}\quad {pitch}\quad {of}\quad {pattern}\quad 12} \right)}} \\{= {\lambda/\left( {0.75{\lambda/{NA}}} \right)}} \\{= {{NA}/0.75}}\end{matrix}$

and since the incident beams Lil and Lir are initially apart by 2NA/1.5from each other, at the Fourier transform plane of the projectionoptical system 13 the diffracted beams Ll0 and Lr1 pass through the samefirst optical path, whereas the diffracted beams Lr0 and Ll1 passthrough the same second optical path. In this case, the first and secondoptical paths are symmetrically apart by the equal distance from theoptical axis of the projection optical system 13.

FIG. 6a shows schematically the intensity distribution of the diffractedbeams at the Fourier transform plane 14 of the projection optical system13. In FIG. 6a, a spot 22 l formed at the Fourier transform plane 14 isthe result of the convergence of the diffracted beams Lr0 and Ll1 andsimilarly a spot 22 r is one resulting from the convergence of thediffracted beams Ll0 and Lr1.

As will be seen from FIG. 6a, in accordance with the present embodimenteach combination of the 0-order diffracted beam and the +first-order or−first-order diffracted beam from the pattern 12 having a line pitch of0.75λ/NA finer than λ/NA can be condensed almost 100% on the wafer 17through the projection optical system 13, so that even in the case offiner pattern than that pitch (λ/NA) representing the limit to theresolution of the conventional exposure apparatus, the use of thespatial filters having the transparent windows of the dimensionscorresponding to the line pitches of the mask patterns makes it possibleto effect the exposure and transfer with sufficient resolutions.

Referring now to FIG. 5b, there is illustrated a spatial filter which isused in the case of a mask pattern consisting of a line-and-spacepattern crossing in the x and y directions. Also, FIG. 6b shows theconditions of the spots formed in correspondence to the diffracted beamsat the Fourier transform plane of the projection optical system in thecase of FIG. 5b.

Next, the resolution of the pattern on the substrate 17 in the exposureapparatus of the present embodiment will be described in comparison withexposure apparatus according to various reference examples.

=In the Case of Reference Examples=

FIGS. 7 and 8 respectively show schematically the optical pathconstruction of the illuminating light (FIG. 7) and the light quantitydistribution at the Fourier transform plane of the projection opticalsystem (FIG. 8) in the projection exposure apparatus shown in thepreviously mentioned Japanese Laid-Open Patent Application No.2-50417cited as a reference example. It is to be noted that in the Figures thecomponents which are the same in operation and function as in theapparatus according to the above-mentioned embodiment of the presentinvention are designated by the same reference numerals as in FIG. 2.

In FIG. 7, an aperture stop 6A (a spatial filter having a circulartransparent window formed concentrically with the optical axis) isarranged at the Fourier transform plane of the illumination opticalsystem thereby limiting the angle of incidence of the illuminating lighton the mask 11. The 0-order diffracted beam (the solid lines) and the±first-order diffracted beams (the broken lines) produced from thepattern 12 of the mask 11 are both entered into the projection opticalsystem 13 and proceed along separate optical paths so that a spot 20 lof the +first-order diffracted beam, a spot 20 c of the 0-orderdiffracted beam and a spot 20 r of the −first-order diffracted beam areformed at separate positions apart from one another in the Fouriertransform plane 14 as shown in FIG. 8.

Also, FIGS. 9 and 10 respectively show schematically the optical pathconstruction of the illuminating light (FIG. 9) and the light quantitydistribution at the Fourier transform plane of the projection opticalsystem (FIG. 10) in a projection exposure apparatus cited as anotherreference example. In this another reference example, the aperture stop6A of FIG. 7 is replaced with a spatial filter 6B formed with an annulartransparent window which is concentric with the optical axis.

In FIG. 9, provided at the Fourier transform plane of the illuminationoptical system is the spatial filter 6B having the annular transparentwindow formed concentrically with the optical axis so that theilluminating light is obliquely projected or in an inverse conical formonto the mask 11. As a result, at least within the plane traversing theoptical axis in the line pitch direction of the pattern 12, as in thecase of the embodiment of the present invention shown in FIG. 2, the0-order diffracted beam (the solid lines) is obliquely entered like thefirst-order diffracted beams (the broken lines) into the projectionoptical system so that they pass through the projection optical systemwhile partly overlapping the separate first-order diffracted beamsentering from then opposite sides and the reach up to the wafer 17,thereby forming a projected image. At this time, a doughnut shaped spot21 c of the 0-order diffracted beam which is concentric with the opticalaxis as well as a spot 21 l of the ±first-order diffracted beam and aspot 21 r of the −first-order diffracted beam which are adjacent to andpartly overlapping the spot 21 c are formed in the Fourier transformplane 14 of the projection optical system 13 as shown in FIG. 10. Inthis case, the large parts of the spots 21 l and 21 r extend to theoutside of the projection optical system 13 and the beams of theseexternally extended portions are eclipsed by the lens barrel of theprojection optical system.

=In the Case of the Embodiment of the Present Invention=

FIGS. 11 to 14 are diagrams showing the distributions of the lightintensities I of the projected images on the wafer 17 in the embodimentof the present invention shown in FIG. 2 in comparison with the cases ofFIGS. 7 and 9. These light intensities are in conformity with theresults obtained by calculation with respect to within the planetraversing the optical axis in the line pitch direction of the pattern12 on the substrate with the NA of the projection optical system beingselected 0.5, the wavelength λ of the illuminating light selected 0.365μm and the pattern line pitch of the mask pattern 12 selected 0.5 μm(about 0.685×λ/NA) in terms of the value on the wafer 17 obtained fromthe magnification of the projection optical system 13.

FIG. 11 shows the light intensity distribution of the projected imageformed on the substrate by the exposure apparatus according to thepreviously mentioned embodiment (FIG. 2) of the present invention and itwill be seen that this intensity distribution has a sufficientlight-and-dark contrast of the edges of the pattern.

FIG. 12 shows the light intensity distribution of the projected image onthe substrate in the case where the diameter of the aperture stop 6A isrelatively small and the ratio of the numerical aperture of theillumination optical system to the numerical aperture of the projectionoptical system or the so-called σ value is selected 0.5 in the referenceexample of FIG. 7. In this case, it will be seen that since the ratio (σvalue) of the numerical aperture of the illumination optical system tothe numerical aperture of the projection optical system is selected 0.5,the projected image has a flat light intensity distribution withoutpractically any light-and-dark contrast.

FIG. 13 shows the light intensity distribution of the projected image inthe case where the opening of the aperture stop 6A is relatively largeand the ratio of the numerical aperture of the illumination opticalsystem to the numerical aperture of the projection optical system or theso-called σ value is selected 0.9 in the reference example of FIG. 7. Inthis case, it will be seen that while the light-and-dark contrast of theprojected image is greater than in the,case of FIG. 12 due to the factthat the ratio (σvalue) of the numerical aperture of the illuminationoptical system to the numerical aperture of the projection opticalsystem is selected 0.9, the light intensity distribution is stillrelatively large in 0-order diffracted beam component and comparativelyflat and thus it is unsatisfactory from the standpoint of thelight-response characteristic of the resist.

FIG. 14 shows the light intensity distribution of the projected image onthe substrate in the case of the reference example of FIG. 9 and in thiscase the inner and outer edges of the annular transparent window of thespatial filter 6B respectively correspond to 0.7 and 0.9 in terms of theσ value. While this projected image is stronger in light-and-darkcontrast than in the case of FIG. 12, the light intensity distributionis still relatively large in 0-order diffracted beam component andcomparatively flat and thus it is still insufficient from the standpointof the light-response characteristic of the resist.

As will be seen from FIGS. 11 to 14, in accordance with the embodimentof the present invention shown in FIG. 2 the substantial resolution ofthe projected image on the substrate is greatly improved as comparedwith the cases of FIGS. 7 and 9.

Then, in the case of FIG. 9, if a spatial filter of the same type as thespatial filter 15 used in the previously mentioned embodiment issimilarly arranged at the Fourier transform plane of the projectionoptical system 13, the diffracted beams of the 0-order and ±first-orderscan be selectively condensed at the portions indicated by the crosshatching in FIG. 10 so as to slightly improve the resolution of theprojected image on the wafer 17 as compared with the case of FIG. 14. Inthis case, however, there is the unavoidable disadvantage that theutilization rate of the illuminating light incident on the projectionoptical system is decreased greatly and the energy component notcontributing to the exposure is accumulated within the projectionoptical system thereby changing its optical characteristics. In theembodiment of FIG. 2 according to the present invention, practically allthe energy of the illuminating light incident on the projection opticalsystem contributes to the exposure.

Then, even in the past, there has been known the technique of positivelyutilizing the diffracted beams from a mask pattern to improve theresolution of the projection optical system and this technique is suchthat dielectric members for reversing the phase of the illuminatinglight, i.e., the so-called phase shifters are arranged alternately withthe transparent portions of the pattern. However, actually it isextremely difficult to properly provide such phase shifters on acomplicated semiconductor circuit pattern and no inspection method forphase shifted photomasks has been established as yet.

With the embodiment of FIG. 2 according to the present invention, whileits effect of improving the resolution of the projected image iscomparable to that of the phase shifters, it is possible to use aconventional photomask without phase shifters as such and it is possibleto follow the conventional photomask inspection techniques as such.

Also, while the use of the phase shifters has the effect of increasingin effect the focus depth of the projection optical system, even in theembodiment of FIG. 2, as shown in FIG. 6a, the spots 22 l and 22 r atthe Fourier transform plane 14 are in the equidistant positions from thecenter of the pupil so that they are less susceptible to the effect ofthe front wave aberrations due to the defocusing as mentioned previouslyand a large focus depth is obtained.

While, in the above-described embodiment, the mask pattern comprises byway of example a line-and-space pattern which varies regularly in thex-direction, the foregoing effect can be fully attained on the ordinarypatterns other than the line-and-space pattern by combining properspatial filters in the respective cases. Then, while the number of thewindows in the spatial filer is two when the mask pattern has aone-dimensional variation which varies only in the x-direction, in thecase of a pattern having a plurality of n dimensional variations, thenumber of the required transparent windows is 2n in accordance with thespatial frequency of the pattern. For instance, in the case of adiffraction grating pattern having a two-dimensional variation in the xand y directions, for example, as shown in FIG. 5b, it is necessary toform two pairs or a total of four transparent windows arranged on thecross in the spatial filter so that the four corresponding diffractedbeam spots are formed at the Fourier transform plane of the projectionoptical system as shown in FIG. 6b.

Also, while, in the above-described embodiment each of the plates 6 cand 15 c of the spatial filter 6 and 16 is considered as one which doesnot transmit the illuminating light at all for purposes of simplifyingthe description, each of the plates 6 c and 15 c may be constructed as alight attenuating plate having a certain predetermined degree of lighttransmittance so that in this case, only the contrast of a projectedimage of any specified fine pattern can be selectively improved duringthe exposure by the front beam cross-section of the illuminating lightas in the past.

Further, while the description of the embodiment has been made withparticular emphasis on the spatial filter within the illuminationoptical system, it can be considered that the spatial filter within theprojection optical system is basically the same in function and effect.In other words, the same effect can be obtained by arranging a spatialfilter satisfying the above-mentioned conditions at least at one ofsubstantially the Fourier transform plane of the illumination opticalsystem and substantially the Fourier transform plane of the projectionoptical system. Also, as for example, it is possible to arrange aspatial filter such as shown in FIG. 3 at the Fourier transform plane ofthe illumination optical system and a spatial filter having an annulartransparent window at the Fourier transform plane of the projectionoptical system. In this case, it is needless to say that with the latterspatial filter having the annular transparent window, the annulartransparent window must be arranged in such a manner that both of the0-order diffracted beam and the +first-order (or the −first-order)diffracted beam from the mask pattern are passed together through it.Further, by using the two spatial filters in combination, there is theeffect of cutting off the diffused reflection from the projectionoptical system or the wafer and preventing the stray light rays.

Still further, while, in the above-described embodiment, the descriptionis mainly directed to the case where the spatial filters (6, 15) aremechanically changed in dependence on the mask pattern, if, for example,a spatial filter comprising a liquid crystal device, an EC (electrochromic) device or the like is used, there are advantages that not onlythe use of any mechanical filter changing mechanism is eliminated butalso the adjustment and change of the positions of transparent windowsis attained by means of electric circuitry, that the apparatus is mademore compact in size and that the adjustment and change of the size,shape and position of transparent windows can be effected easily and athigh speeds.

The embodiments described herein are for the purpose of illustrationwithout any intention of limitation and the technical scope of thepresent invention is intended to be limited in accordance with thestatement of the appended claims.

What is claimed is:
 1. An exposure apparatus that forms on a substratean image of a pattern having linear features extending in at least apredetermined direction, said apparatus comprising: an illuminationsystem that illuminates the pattern with light having a decreased lightintensity distribution within a portion defined along the predetermineddirection on a pupil plane of the illumination system so that lightbeams from two portions symmetrically located with respect to theportion are directed to the pattern along a pair of paths that aresymmetrically inclined with respect to a plane of incidence includingthe predetermined direction; and a projection optical system to projectthe image of the pattern onto the substrate wherein two diffracted beamsdiffering in order generated from the pattern by irradiation of thelight beams, pass through a same area on a pupil plane of the projectionoptical system substantially conjugate with one of the two portions. 2.An apparatus according to claim 1, wherein said illumination systemincludes a stop member having a light shielding section that covers saidportion defined along said predetermined direction.
 3. An apparatusaccording to claim 1, wherein said illumination system includes anoptical integrator and forms said decreased light intensity distributionat or in a vicinity of an exit end of the optical integrator.
 4. Anapparatus according to claim 1, wherein said projection optical systemhas a filter member at or in a vicinity of the pupil plane of saidprojection optical system.
 5. A semiconductor device manufactured byusing an apparatus as defined in claim
 1. 6. An apparatus for imaging apattern having linear features extending in at least a predetermineddirection, said apparatus comprising: an illumination optical system forilluminating the pattern with light from a secondary light source havinga decreased light intensity portion defined along the predetermineddirection and including an optical axis of the illumination opticalsystem on a pupil plane of the illumination optical system so that lightbeams from two portions symmetrically located with respect to thedecreased light intensity portion are directed to the pattern along apair of paths that are symmetrically inclined with respect to a plane ofincidence including the predetermined direction; and a projectionoptical system to project an image of the pattern onto a predeterminedplane; wherein two diffracted beams differing in order generated fromthe pattern by irradiation of the light beams, pass through a same areaon a pupil plane of the projection optical system substantiallyconjugate with one of the two portions.
 7. An apparatus according toclaim 6, wherein an intensity at said decreased light intensity portionis decreased to about zero.
 8. An apparatus according to claim 6,wherein said illumination optical system includes an optical integratorthat forms said secondary light source and a stop member having at leasttwo apertures to define said decreased light intensity portion.
 9. Anexposure apparatus that forms on a substrate an image of a patternhaving linear features extending in at least a predetermined direction,said apparatus comprising: an illumination system that illuminates thepattern with light having a decreased light intensity distributionrelative to two portions located in a direction perpendicular to thepredetermined direction on a pupil plane of the illumination system sothat light beams from the two portions are directed to the pattern alonga pair of paths that are symmetrically inclined with respect to a planeof incidence including the predetermined direction; and a projectionoptical system to project the image of the pattern onto the substrate;wherein two diffracted beams differing in order generated from thepattern by irradiation of the light beams, pass through a same area on apupil plane of the projection optical system substantially conjugatewith one of the two portions.
 10. An exposure apparatus that forms on asubstrate an image of a pattern having linear features extending in atleast a predetermined direction, said apparatus comprising: anillumination system that illuminates the pattern with light having anincreased light density distribution within at least two sectionsrelative to a portion defined along the predetermined direction on apupil plane of the illumination system so that light beams from the atleast two sections are directed to the pattern along at least one pairof paths that are symmetrically inclined with respect to a plane ofincidence including the predetermined direction; and a projectionoptical system to project the image of the pattern onto the substrate;wherein two diffracted beams differing in order generated from thepattern by irradiation of the light beams, pass through a same area on apupil plane of the projection optical system substantially conjugatewith one of the at least two sections.
 11. An exposure apparatus thatforms on a substrate an image of a pattern having linear featuresextending in at least a predetermined direction, said apparatuscomprising: an illumination system that illuminates the pattern withlight having a decreased light intensity distribution within a portiondefined along the predetermined direction on a pupil plane of theillumination system so that light beams from two portions symmetricallylocated with respect to the portion are directed to the pattern along apair of paths that are symmetrically inclined with respect to a plane ofincidence including the predetermined direction, said illuminationsystem including a first filter to form the decreased light intensitydistribution; and a projection optical system for projecting the imageof the pattern onto the substrate through a second filter arranged at orin a vicinity of a Fourier transform plane of the projection opticalsystem; wherein two diffracted beams differing in order generated fromthe pattern by irradiation of the light beams, pass through a same areaon the Fourier transform plane substantially conjugate with one of thetwo portions.
 12. A method of exposing a substrate through a projectionoptical system with a pattern having linear features extending in atleast a predetermined direction, the method comprising: illuminating thepattern with light along a pair of paths that are symmetrically inclinedwith respect to a plane of incidence including the predetermineddirection; and projection an image of the pattern onto the substrate;wherein a first diffracted beam generated from the pattern byirradiation of light along one path of the pair of paths and a seconddiffracted beam having different order from that of the first diffractedbeam and generated from the pattern by irradiation of light alonganother path of the pair of paths, pass through a same area on a pupilplane of the projection optical system and apart from the optical axisthereof.
 13. An apparatus that exposes an object with a pattern havinglinear features extending in at least a predetermined direction, theapparatus comprising: an illumination system that illuminates thepattern with light along a pair of paths that are symmetrically inclinedwith respect to a plane of incidence including the predetermineddirection from at least two apertures provided on a stop and separatedby a light shielding or light attenuating portion along thepredetermined direction; and a projection optical system that projectsan image of the pattern onto the object; wherein two diffracted beamsdiffering in order generated from the pattern by irradiation of thelight along the pair of paths, pass through a same area on a pupil planeof the projection optical system substantially conjugate with one of theat least two apertures.
 14. An apparatus that exposes an object with apattern having linear features extending in at least a predetermineddirection, the apparatus comprising: an illumination system thatilluminates the pattern with light along a pair of paths that aresymmetrically inclined with respect to a plane of incidence includingthe predetermined direction passing through a stop that substantiallyblocks light along a path in a plane of incidence including thepredetermined direction; and a projection optical system that projectsan image of the pattern onto the object wherein a first diffracted beamgenerated from the pattern by irradiation of light along one path of thepair of paths and a second diffracted beam having different order fromthat of the first diffracted beam and generated from the pattern byirradiation of light alone another path of the pair of paths, passthrough a same area on a pupil plane of the projection optical systemand apart from the optical axis thereof.
 15. An exposure apparatuscomprising: a light source; a light condensing optical system thatcondenses light from said light source and applies the condensed lightto a mask having a periodic pattern; a projection optical system thatprojects an image of said pattern illuminated by said condensed lightonto a substrate; and an aperture member interposed between said lightsource and said mask, said aperture member being provided with twolocalized light transmitting areas arranged along a periodic directionof said periodic pattern so that light beams from two localized lighttransmitting areas are directed to the pattern along a pair of pathsthat are symmetrically inclined with respect to a plane of incidenceincluding a direction perpendicular to the periodic direction; whereintwo diffracted beams differing in order generated from the periodicpattern by irradiation of the light beams, pass through a same area on apupil plane of the projection optical system substantially conjugatewith one of the two localized light transmitting areas.
 16. An exposureapparatus comprising: an illumination optical system that illuminates apattern of a mask with light beams along a pair of paths that aresymmetrically inclined with respect to a plane of incidence including adirection perpendicular to a periodic direction of the pattern from atleast two apertures of a stop, each aperture providing a localized lighttransmitting area and being spaced, in the periodic direction, from anoptical axis of the illumination optical system; and a projectionoptical system that projects an image of the pattern onto apredetermined plane; wherein two diffracted beams differing in ordergenerated from the pattern by irradiation of the light beams, passthrough a same area on a pupil plane of the projection optical systemsubstantially conjugate with one of the at least two apertures.
 17. Anapparatus according to claim 16, wherein said illumination opticalsystem has an optical integrator, said stop being adjacent to theoptical intergrator.
 18. An apparatus according to claim 16, whereinsaid stop has four apertures arranged at intervals of 90 degrees withrespect to the optical axis of said illumination optical system.
 19. Amethod of exposing a substrate with a pattern on a mask, comprising:arranging a stop having at least two apertures within an illuminationsystem that illuminates the pattern with light beams from the aperturessuch that two of the apertures that define a pair of paths symmetricallyinclined with respect to a plane of incidence including a directionperpendicular to a periodic direction of the pattern, are arranged alongthe periodic direction and apart from an optical axis of theillumination system; and forming an image of the pattern onto thesubstrate through a projection optical system; wherein two diffractedbeams differing in order generated from the pattern by irradiation ofthe light beams, pass through a same area on a pupil plane of theprojection optical system substantially conjugate with one of theapertures.
 20. An apparatus that transfers a pattern, formed on a mask,having linear features extending in a predetermined direction onto asubstrate, comprising: an illumination optical system of which aplurality of optical elements are arranged along an optical axisperpendicular to the mask to illuminate the mask with light along a pairof paths that are symmetrically inclined with respect to a plane ofincidence including the optical axis and the predetermined direction;and a projection optical system disposed between the mask and thesubstrate to project light onto the substrate through the mask; whereina first diffracted beam generated from the pattern by irradiation oflight along one path of the pair of paths and a second diffracted beamhaving different order from that of the first diffracted beam andgenerated from the pattern by irradiation of light along another path ofthe pair of paths, pass through a same area on a pupil plane of theprojection optical system and apart form the optical axis thereof. 21.An exposure apparatus comprising: an illumination optical system,disposed on an optical path through which light from a light sourcepasses to illuminate a mask with the light, that forms differentintensity distributions of the light on a predetermined plane in theillumination optical system, one of the different intensitydistributions having increased intensity portions apart from an opticalaxis of the illumination optical system relative to a portion on theoptical axis, of which first distances from the optical axis aresubstantially equal in a direction perpendicular to a linear featureilluminated with the light; and a projection optical system, having anoptical axis that is aligned with the optical axis of the illuminationoptical system, to image a pattern on the mask onto an object; whereinthe predetermined plane in the illumination optical system issubstantially conjugate with a pupil plane of the projection opticalsystem, and two diffracted beams differing in order generated from thepattern by irradiation of light from each of the increased intensityportions, pass through different areas on the pupil plane of theprojection optical system and apart from the optical axis of theprojection optical system, of which second distances from the opticalaxis of the projection optical system are substantially equal when thepattern includes the linear feature.
 22. An apparatus according to claim21, wherein said first distances are determined in accordance with afineness of said linear feature.
 23. An apparatus according to claim 22,wherein said illumination optical system includes a first optical devicedisposed on said optical path and a second optical device exchanged forthe first optical device to form said different intensity distributionsof the light.
 24. An apparatus according to claim 22, wherein a firstdiffracted beam generated from said linear feature by irradiation oflight from a first one of said increased intensity portions and a seconddiffracted beam having a different order from that of the firstdiffracted beam and generated from said linear feature by irradiation oflight from a second one of said increased intensity portions differentfrom the first increased intensity portion, substantially pass through asame one of said different areas on the pupil plane of said projectionoptical system and apart from the optical axis thereof.
 25. An apparatusaccording to claim 21, wherein positions of said increased intensityportions on said predetermined plane are determined in accordance with aFourier transformed pattern of the pattern on said mask.
 26. Anapparatus according to claim 25, wherein said increased intensityportions are arranged at or in a vicinity of middle positions betweenthe optical axis of said illumination optical system and peak positionsof said Fourier transformed pattern.
 27. An apparatus according to claim26, wherein said increased intensity portions are arranged at or in avicinity of a part of said middle positions determined in accordancewith a numerical aperture of said projection optical system.
 28. Anapparatus according to claim 26, wherein the number of said increasedintensity portions is 2n (n is a natural number).
 29. An apparatusaccording to claim 21, wherein said one intensity distribution has 2nincreased intensity portions (n is a natural number).
 30. An apparatusaccording to claim 29, wherein said illumination optical system includesa first optical device disposed on said optical path and a secondoptical device exchanged for the first optical device to form saiddifferent intensity distributions of the light.
 31. An apparatusaccording to claim 29, wherein a first diffracted beam generated fromsaid linear feature by irradiation of light from a first one of saidincreased intensity portions is distributed at one of said differentareas on the pupil plane of said projection optical system through whichat least part of a second diffracted beam, having a different order fromthat of the first diffracted beam, generated from said linear feature byirradiation of light from a second one of said increased intensityportions different from the first increased intensity portion passes.32. An apparatus according to claim 1, wherein said two diffracted beamscomprise a 0-order diffracted beam generated from said pattern byirradiation of a light beam from one of said two portions and afirst-order diffracted beam generated from said pattern by irradiationof a light beam from another of said two portions.
 33. An apparatusaccording to claim 32, wherein said two portions are located asubstantially same distance from an optical axis of said illuminationsystem on the pupil plane of said illumination system.
 34. An apparatusaccording to claim 6, wherein said two diffracted beams comprise a0-order diffracted beam generated from said pattern by irradiation of alight beam from one of said two portions and a first-order diffractedbeam generated from said pattern by irradiation of a light beam fromanother of said two portions.
 35. An apparatus according to claim 9,wherein said two diffracted beams comprise a 0-order diffracted beamgenerated from said pattern by irradiation of a light beam from one ofsaid two portions and a first-order diffracted beam generated from saidpattern by irradiation of a light beam from another of said twoportions.
 36. An apparatus according to claim 10, wherein said twodiffracted beams comprise a 0-order diffracted beam generated from saidpattern by irradiation of a light beam from a first one of said at leasttwo sections and a first-order diffracted beam generated from saidpattern by irradiation of a light beam from a second one of said atleast two sections different from the first section.
 37. An apparatusaccording to claim 11, wherein said two diffracted beams comprise a0-order diffracted beam generated from said pattern by irradiation of alight beam from one of said two portions and a first-order diffractedbeam generated from said pattern by irradiation of a light beam fromanother of said two portions.
 38. A method according to claim 12,wherein one of said first and second diffracted beams is a 0-orderdiffracted beam and another of said first and second diffracted beams isa first-order diffracted beam.
 39. An apparatus according to claim 13,wherein said two diffracted beams comprise a 0-order diffracted beamgenerated from said pattern by irradiation of light along one path ofsaid pair of paths and a first-order diffracted beam generated from saidpattern by irradiation of light along another path of said pair ofpaths.
 40. An apparatus according to claim 14, wherein one of said firstand second diffracted beams is a 0-order diffracted beam and another ofsaid first and second diffracted beams is a first-order diffracted beam.41. An apparatus according to claim 15, wherein said two diffractedbeams comprise a 0-order diffracted beam generated from said pattern byirradiation of a light beam from one of said two localized lighttransmitting areas and a first-order diffracted beam generated from saidpattern by irradiation of a light beam from another of said twolocalized light transmitting areas.
 42. An apparatus according to claim16, wherein said two diffracted beams comprise a 0-order diffracted beamgenerated from said pattern by irradiation of a light beam along onepath of said pair of paths and a first-order diffracted beam generatedfrom said pattern by irradiation of a light beam along another path ofsaid pair of paths.
 43. A method according to claim 19, wherein said twodiffracted beams comprise a 0-order diffracted beam generated from saidpattern by irradiation of a light beam from one of said two aperturesand a first-order diffracted beam generated from said pattern byirradiation of a light beam from another of said two apertures.
 44. Anapparatus according to claim 20, wherein one of said first and seconddiffracted beams is a 0-order diffracted beam and another of said firstand second diffracted beams is a first-order diffracted beam.
 45. Anapparatus according to claim 31, wherein said predetermined plane issubstantially a pupil plane of said illumination optical system, and oneof said first and second diffracted beams is a 0-order diffracted beamand another of said first and second diffracted beams is a first-orderdiffracted beam.
 46. An apparatus according to claim 21, wherein saidpredetermined plane is substantially a pupil plane of said illuminationoptical system, and said two diffracted beams comprise a 0-orderdiffracted beam and a first-order diffracted beam.
 47. An apparatusaccording to claim 46, wherein said increased intensity portions arearranged at or in a vicinity of middle positions between the opticalaxis of said illumination optical system and peak positions of a Fouriertransformed pattern of the pattern on said mask.
 48. An apparatusaccording to claim 46, wherein said illumination optical system includesa first optical device disposed on said optical path and a secondoptical device exchanged for the first optical device to form saiddifferent intensity distributions of the light.